Known forms of transporting webs use straight, non-variable cylindrical rollers. These rollers, however, compromise wrinkle formation and are designed for limited tension ranges and thread path conditions. To reduce this wrinkle formation, an anti-wrinkle roller is often used as a steering roller in a web line. However, known anti-wrinkle rollers compromise guiding by increasing lateral instability of the web. These rollers are always spreading the web, requiring a separate downstream device to steer the web. Also, some of these rollers have a limited range of wrap angles over which they are effective.
There are two types of anti-wrinkle rollers, both of which spread the web in the width direction to smooth out wrinkles. The first type spreads the web before it enters the roller by inducing crossweb lateral tensions in the span immediately upstream of the roller. Curved axis rollers (also referred to as bowed or banana rollers) and reverse crown rollers are of this type. The second type spreads the web after it contacts the roller surface, through spreading action from some form of crossweb expansion of the roller surface. Roller surface expansion comes from mechanisms that induce lateral expanding of slats or flexible roller covering, or from machined grooves in the roller surface that create an outward, axial expansion when deflected by radial compression of the web as it wraps the roller surface.
Some known rollers use circumferential spiral grooves which are intended to stretch the web.